The connection between things that happen on the sun and things that happen on the earth has been manifest for so long that the sun has often been worshipped as a god with power over terrestrial destinies. Since the dawning of the scientific age, the connections have been regarded as more physical than supernatural, but a number of them have been long-standing mysteries nevertheless. One such mysterious connection is the relation between certain disturbances in earth's magnetic field that appeared to have a 27-day period like the rotation of the sun and solar conditions. It appears, according to A. J. Hundhausen of the High Altitude Observatory of the National Center for Atmospheric Research at Boulder, Colo., that these geomagnetic phenomena are connected to solar magnetism, and the linkage goes by way of the solar wind and a recently discovered phenomenon, holes in the solar corona. One of the possible results of this discovery, Hundhausen remarked in a summary presentation he gave at the recent meeting of the Plasma Physics Division of the American Physical Society at San Francisco, is that scientists may be able to study changes in solar magnetism by means of geomagnetic data. These particular geomagnetic disturbances tend to occur near the end of each 11 -year cycle of solar activity, and their appearance has been recorded for quite some time. At one point, Hundhausen uses the phrase "as in 1859" to describe, them. Attempted explanations came somewhat later than that. Plausible ones date from the early years of this century. The hypothesis was proposed that there were particular regions on the sun that were somehow responsible for the geomagnetic disturbances and that were carried around by the sun, hence the correlation with the sun's 27-day rotation period. As the nature of subatomic particles and their interactions with electric and magnetic fields became clear, it was suggested that these regions on the sun emitted bursts of protons that affected the earth's magnetic field. These solar regions were dubbed M regions, and, says Hundhausen, "People worked for 40 years" to elucidate the nature of the M regions "and got nowhere. " Then came the discovery of the solar wind and the decade of the 1960s. It was clear then that the sun emits protons, but it does it all the time, not in bursts. Still there are differences. There are fast and slow streams in the solar wind, the fast ones coming at rates around 600 kilometers per second. The differences in solar wind speed seemed related to the configObservations of holes in the sun's corona help explain fluctuations in solar magnetism